Real time eye tracking for human computer interaction

ABSTRACT

A gaze direction determining system and method is provided. A two-camera system may detect the face from a fixed, wide-angle camera, estimates a rough location for the eye region using an eye detector based on topographic features, and directs another active pan-tilt-zoom camera to focus in on this eye region. A eye gaze estimation approach employs point-of-regard (PoG) tracking on a large viewing screen. To allow for greater head pose freedom, a calibration approach is provided to find the 3D eyeball location, eyeball radius, and fovea position. Both the iris center and iris contour points are mapped to the eyeball sphere (creating a 3D iris disk) to get the optical axis; then the fovea rotated accordingly and the final, visual axis gaze direction computed.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of U.S. patent applicationSer. No. 14/537,173, filed Nov. 10, 2014 (allowed), which is aContinuation of U.S. patent application Ser. No. 13/549,730, filed Jul.16, 2012, now U.S. Pat. No. 8,885,882, issued Nov. 11, 2014, whichclaims benefit of priority from U.S. Provisional Patent Application Ser.No. 61/507,780, filed Jul. 14, 2011, the entirety of which are expresslyincorporated herein by reference.

GOVERNMENT RIGHTS CLAUSE

This invention was made with government support under FA8750-08-0096awarded by the United States Air Force. The government has certainrights in the invention.

BACKGROUND OF THE INVENTION

The ideal human-computer interaction system should function robustlywith as few constraints as those found in human-to-human interaction.One of the most effective means of interaction is through the behaviorof the eye. Specifically, knowledge of the viewing direction and thusthe area of regard offers insight into the user's intention and mentalfocus, and consequently this information is vital for the nextgeneration of user interfaces [21][22]. Applications in this vein can befound in the fields of HCI, security, advertising, psychology, and manyothers [5][21].

As such, there has been intensive research on eye tracking and gazeestimation for the past 30 years [5]. However, with the conventionalsingle-camera system, either the user must keep his or her head lockedin place (so that it remains within the narrow field of view), thecamera must be strapped to the subject's head (a common approach for eyedetection), or some other marker (like a small infrared light) must beworn by the subject [2]. The resulting situation can be prodigiouslyinconvenient and uncomfortable for the user. Because of the uniquereflective properties of the pupil to infrared (IR) light, some systemshave opted to detect the face by first finding the eyes [2][10][11].While robust to visible light conditions, these methods have issues withchanges in head pose, reflections off glasses, and even decreasedreflectivity of the retina from contact lenses [9]. An alternativeapproach is to use stereo cameras [2][11]; while robust, these systemsgenerally require substantial calibration time. Some complex systems(like “smart rooms” [1]) require expensive and/or non-portable setups.Even existing, non-stereo, two-camera systems [16] often restrict theuser to a preset location in the room.

The overwhelming majority of gaze estimation approaches rely on glints(the reflection of light off the cornea) to construct 2D or 3D gazemodels [5]. Alternatively, eye gaze may be determined from the pupil oriris contours [18] using ellipse fitting approaches [3][15]. One canalso leverage the estimated iris center directly and use its distancefrom some reference point (e.g., the eye corners) for gaze estimation[12][19]. Indeed, the entire eye region may be segmented into the iris,sclera (white of the eye), and the surrounding skin; the resultingregions can then be matched pixel-wise with 3D rendered eyeball models(with different parameters) [17][20]. However, different subjects, headpose changes, and lighting conditions could significantly diminish thequality of the segmentation [20].

U.S. Pat. No. 8,077,217 provides an eyeball parameter estimating deviceand method, for estimating, from a camera image, as eyeball parameters,an eyeball central position and an eyeball radius which are required toestimate a line of sight of a person in the camera image. An eyeballparameter estimating device includes: a head posture estimating unit forestimating, from a face image of a person photographed by a camera,position data corresponding to three degrees of freedom (x-, y-, z-axes)in a camera coordinate system, of an origin in a head coordinate systemand rotation angle data corresponding to three degrees of freedom (x-,y-, z-axes) of a coordinate axis of the head coordinate system relativeto a coordinate axis of the camera coordinate system, as head posturedata in the camera coordinate system; a head coordinate system eyeballcentral position candidate setting unit for setting candidates ofeyeball central position data in the head coordinate system based oncoordinates of two feature points on an eyeball, which are preliminarilyset in the head coordinate system; a camera coordinate system eyeballcentral position calculating unit for calculating an eyeball centralposition in the camera coordinate system based on the head posture data,the eyeball central position candidate data, and pupil central positiondata detected from the face image; and an eyeball parameter estimatingunit for estimating an eyeball central position and an eyeball radiusbased on the eyeball central position in the camera coordinate system soas to minimize deviations of position data of a point of gaze, a pupilcenter, and an eyeball center from a straight line joining originalpositions of the three pieces of position data.

U.S. Pat. No. 7,306,337, expressly incorporated herein by reference,determines eye gaze parameters from eye gaze data, including analysis ofa pupil-glint displacement vector from the center of the pupil image tothe center of the glint in the image plane. The glint is a small brightspot near the pupil image resulting from a reflection of infrared lightfrom a an infrared illuminator off the surface of the cornea.

U.S. Pat. Pub. 2011/0228975, expressly incorporated herein by reference,determines a point-of-gaze of a user in three dimensions, by presentinga three-dimensional scene to both eyes of the user; capturing image dataincluding both eyes of the user; estimating line-of-sight vectors in athree-dimensional coordinate system for the user's eyes based on theimage data; and determining the point-of-gaze in the three-dimensionalcoordinate system using the line-of-sight vectors. It is assumed thatthe line-of-sight vector originates from the center of the corneaestimated in space from image data. The image data may be processed toanalyze multiple glints (Purkinje reflections) of each eye.

U.S. Pat. No. 6,659,611, expressly incorporated herein by reference,provides eye gaze tracking without calibrated cameras, directmeasurements of specific users' eye geometries, or requiring the user tovisually track a cursor traversing a known trajectory. One or moreuncalibrated cameras imaging the user's eye and having on-axis lighting,capture images of a test pattern in real space as reflected from theuser's cornea, which acts as a convex spherical mirror. Parametersrequired to define a mathematical mapping between real space and imagespace, including spherical and perspective transformations, areextracted, and subsequent images of objects reflected from the user'seye through the inverse of the mathematical mapping are used todetermine a gaze vector and a point of regard.

U.S. Pat. No. 5,818,954 expressly incorporated herein by reference,provides a method that calculates a position of the center of theeyeball as a fixed displacement from an origin of a facial coordinatesystem established by detection of three points on the face, andcomputes a vector therefrom to the center of the pupil. The vector andthe detected position of the pupil are used to determine the visualaxis.

U.S. Pat. No. 7,963,652, expressly incorporated herein by reference,provides eye gaze tracking without camera calibration, eye geometrymeasurement, or tracking of a cursor image on a screen by the subjectthrough a known trajectory. See also, U.S. Pat. No. 7,809,160, expresslyincorporated herein by reference. One embodiment provides a method fortracking a user's eye gaze at a surface, object, or visual scene,comprising: providing an imaging device for acquiring images of at leastone of the user's eves: modeling, measuring, estimating, and/orcalibrating for the user's head position: providing one or more markersassociated with the surface, object, or visual scene for producingcorresponding glints or reflections in the user's eyes; analyzing theimages to find said glints or reflections and/or the pupil: anddetermining eye gaze of the user upon a said one or more marker asindicative of the user's eye gaze at the surface, object, or visualscene.

One application of eye gaze tracking is in small or large surfaces,particularly large displays or projected wall or semi-transparentsurfaces, including but not limited to LCD screens, computer screens,SMART boards, tabletop displays, projection screens of any type, plasmadisplays, televisions, any computing appliance, including phones, PDAs,and the like, and head-mounted and wearable displays and the like. Inaddition, any surface, including, for example, walls, tables, furniture,architectural ornaments, billboards, windows, semi-transparent screens,window displays, clothing racks, commercial displays, posters, stands,any commercial or other goods, clothing, car dashboards, car windows,and the like, may be the gaze target.

By augmenting any shopping display, such as, for example, computer ortelevision screen-based, projected, static surface, objects, goods(e.g., clothing, furniture), with eye gaze determination, eye gazebehavior of subjects (i.e., shoppers) can be tracked for the purpose ofregistering whether individuals are interested in the goods on display.This can be used for evaluating the design or arrangement ofadvertisements or arrangements of goods, or for disclosing moreinformation about products or objects to the subject. The followingscenario illustrates this application. A clothes rack is augmented withone or more eye tracking cameras, and the clothes or hangers (or anyother goods). Cameras detect which item the shopper is interested in bytracking the eye gaze of the shopper. According to one option, when theduration of an eye fixation on an object reaches a threshold, aprojection unit displays more information about the goods.Alternatively, in response to a fixation, the subject may be addressedusing a recorded message or synthesized computer voice associated withthe object of interest, which acts as an automated sales assistant.Alternatively, information about user interest in an article oradvertisement may be conveyed to a sales assistant or third party.

Interactive or non-interactive home appliances can be augmented usingeye tracking, to determine the availability of users for communicationswith other people or devices. Subjects may direct the target of speechcommands to the appliance, or initiate speech dialogue or other forms ofdisclosure by the appliance through establishing eye gaze fixation withthe appliance.

Eye tracking may be incorporated into a gaming device, portable orotherwise, may provide extra channels of interaction for determininginterest in embodied gaming characters. Characters or objects in gamescan then observe whether they are being looked at by the user and adjusttheir behavior accordingly, for example by avoiding being seen or byattracting user attention. Alternatively, characters or objects canrespond verbally or nonverbally to fixations by the user, engaging theuser in verbal, nonverbal, textual, graphical, or other forms ofdiscourse. In the case of speech recognition agents or online humaninterlocutors, the discourse can be mutual. Alternatively, thetechnology can be used to allow gaming applications to make use of eyegaze information for any control purpose, such as moving on-screenobjects with the eyes, or altering story disclosure or screen-playelements according to the viewing behavior of the user. In addition, anyof the above may be incorporated into robotic pets, board games, andtoys, which may operate interactively at any level.

By incorporating eye tracking into a television display or billboard(e.g., a screen, paper, or interactive display), broadcasters and/oradvertisers can determine what (aspects of) advertisements are viewedby, and hence of interest to, a subject. Advertisers may use thisinformation to focus their message on a particular subject or perceivedinterest of that subject, or to determine the cost per view of theadvertisement, for example, but not limited to, cost per minute ofproduct placements in television shows. For example, this method may beused to determine the amount of visual interest in an object or anadvertisement, and that amount of interest used to determine a fee fordisplay of the object or advertisement. The visual interest of a subjectlooking at the object or advertisement may be determined according tothe correlation of the subject's optical axis with the object over apercentage of time that the object is on display. In addition, themethod may be used to change the discourse with the television, or anyappliance, by channeling user commands to the device or part of thedisplay currently observed. In particular, keyboard or remote controlcommands can be routed to the appropriate application, window or deviceby looking at that device or window, or by looking at a screen or objectthat represents that device or window. In addition, TV content may bealtered according to viewing patterns of the user, most notably byincorporating multiple scenarios that are played out according to theviewing behavior and visual interest of the user, for example, bytelling a story from the point of view of the most popular character.Alternatively, characters in paintings or other forms of visual displaymay begin movement or engage in dialogue when receiving fixations from asubject user. Alternatively, viewing behavior may be used to determinewhat aspects of programs should be recorded, or to stop, mute or pauseplayback of a content source such as DVD and the like.

Eye tracking technology can be used to control the location, size,transparency, shape, or motion of visible notification dialogs on largeor small screens according to viewing behavior of the user. Inparticular, on large screens the technology allows the establishment ofperipheral vision boundaries of the user's eyes, ensuring that a windowis placed in view. On small screens, notification windows can be placedout of the way of the user's foveal vision, and can be acknowledged andremoved after the user has viewed them. In addition, the control of anyhidden or visible cursor on a display can be used to communicateattention to underlying applications or systems. In addition, activationand zooming or resizing of focus windows, and the reorganization ofwindows on a display, can be implemented according to the viewingbehavior of the user or the movement of the user in front of thedisplay. The latter may be accomplished by allowing users to look at thesubsequent focus window, after which a key is pressed to activate thiswindow and make it the front window. This may incorporate zooming of thefront window according to an elastic tiled windowing algorithm, orfisheye view zoom of the front window. In addition, the disclosing ofattention of others for notes on a public display board, by modulatingaspects of size, shape or color of displayed notes, may be accomplishedaccording to the number of times they have been viewed.

Eye tracking can be used to make the content of a display visible onlyto the current user, by using eye fixations to position agaze-contingent blurring lens, directional lens, or obstruction thatprojects the image at the fixation point of that user but not elsewhere.This results in a screen that can only be read by the current user, andnot by any other onlooker. Alternatively, the state of the screen may bealtered by, for example, but not limited to, darkening, wiping, orchanging its contents. Further, visual or auditory notification may beprovided upon detecting more than one pair of eyes looking at thedisplay. This is particularly useful when computing devices are used inpublic, for private matters. Eye tracking may also be used to modulatetransparency of surfaces, for example, but not limited to, cubiclewalls, upon orientation or co-orientation of the eyes, face(s), orhead(s) of a subject or subjects towards that surface.

Eye tracking may also be used in advanced hearing aids to provide aiminginformation for directional microphones or noise cancelling microphones.

Eye tracking may be incorporated invisibly and without restrictions intovehicles to control dashboard or instrument cluster operation, to alterlighting conditions of vehicle illumination or dashboard indicators andinstruments, to reduce impact on visual attention. Displays (includingprojections on windows) may be altered according to viewing behavior,for example, to ensure that eyes remain focused on the road, or todirect the destination of speech commands to appliances or objectswithin or outside the vehicle. In addition, the detection of fatigue,the operation of vehicle navigation systems, entertainment systems,visual display units including video or televisions, the selection ofchannels on a radio or entertainment system, and the initiation andmanagement of remote conversations may all be carried out using theinvention, according to the visual attention of the user.

Eye tracking may be used for sensing attention in remote or same-placemeetings, for editing recordings of such meetings, or for the purpose ofdetecting presence or initiating interactions with remote or co-presentattendees, or for communicating attendee attention in order to optimizea turn taking process among several remote attendees.

Eye tracking may also be used for sensing user attention towards anymobile or portable computing device to determine when a user is payingattention to the visual information provided on the device. Audiovisualmedia played on the device may be paused or buffered automatically uponthe user looking away from the device. The device may continue playingthe buffered audiovisual stream whenever the user resumes looking at thedevice. For example, a mobile device may provide speed readingfacilities. The device streams words across a display screen in a timedmanner, allowing the user to read without producing fixations. When theuser looks away, the stream of words is paused, and when the user looksback at the device, the stream of words continues.

Eye contact sensing objects provide context for action, and therefore aprogrammable system may employ eye tracking or gaze estimation todetermine context. A display may be presented, optimized to presentdifferent available contexts, from which the user may select by simplylooking. When there are multiple contexts, or hybrid contexts, the usermay have a complex eye motion pattern which can be used to determinecomplex contexts.

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SUMMARY OF THE INVENTION

The ability to capture the direction the eyes point in while the subjectis a distance away from the camera offers the potential for intuitivehuman-computer interfaces, allowing for a greater interactivity, moreintelligent behavior, and increased flexibility. A system is providedthat detects the face from a fixed, wide-angle camera, estimates a roughlocation for the eye region using an eye detector based on topographicfeatures, and directs another active pan-tilt-zoom camera to focus in onthis eye region. An eye gaze estimation approach is also provided forpoint-of-regard (PoG) tracking on a large viewing screen. To allow forgreater head pose freedom, a calibration approach is provided to findthe 3D eyeball location, eyeball radius, and fovea position. Moreover,both the iris center and iris contour points are mapped to the eyeballsphere (creating a 3D iris disk) to get the optical axis; the fovea isthen rotated accordingly, and the final, visual axis gaze directioncomputed. This gaze estimation approach may be integrated into atwo-camera system, permitting natural, non-intrusive, pose-invariantpoint of gaze (PoG) estimation in distance, and allowing usertranslational freedom without resorting to infrared or complex hardwaresetups such as stereo-cameras or “smart rooms.”

According to various embodiments of the invention, a system and methodis provided that robustly locates the face from a wide-angle camera view(as well as a rough approximation of the eye positions) and uses thisinformation to guide a pan-tilt-zoom camera to focus in on the eye areaof the detected face. This allows the user translational freedomrelative to the camera, and a simple adjustment of parameters alsopermits varied movement in depth freedom. The system differs from themajority of other systems in this vein in that we do not use infrared,stereo-cameras, specially-constructed hardware (like Noureddin et al.[10]), or specific room setups (i.e. “smart rooms”). This system andmethod are useful for gaze and PoG (Point-of-Regard) estimation.

To bypass the issue of the diminished accuracy of iris centers fromvisible light imagery while simultaneously avoiding the problems heir tothe potential instability of iris contour extraction, both are leveragedto determine eye gaze direction with a 3D eyeball model. The 3D eyeballcenters, radii, and fovea points are calculated through a uniquecalibration approach. During gaze estimation, both the estimated iriscenter and the iris contour points are mapped onto the eyeball sphere.After converting these points into vectors starting at the eyeballcenter, a least-squares approach (or other optimization scheme) may beused to find a vector that is at a known angle from the contour vectorswhile also being approximately in line with the center vector. Thecurrent position of the fovea is found, which is dependent on therotation of the eye, a new iris center computed from the initial gazevector, and the vector from the fovea to this new iris center used asthe final gaze direction. This approach differs from the majority ofprevious techniques, in that the 2D contour pixels are mapped onto theknown 3D eyeball; in contrast, most approaches in this vein project the3D model into the 2D plane.

The aforementioned camera system is preferably integrated with the gazeand PoG (Point-of-Regard) estimation approach.

The process may comprise the following steps, in combination orsub-combination:

An image is captured, and a face detected.

Once the face is detected (or perhaps directly, without antecedent facedetection), eye detection is performed, for example using the so-calledtopographic features of eyes. A pan-tilt-zoom camera may be directed atthe approximate center of the two detected eye candidates, and thecentroid tracked over a series of frames.

According to a preferred embodiment, the red channel of a color videoimage is analyzed, since the iris generally has very low red intensityvalues. The image (i.e., the red channel) is then searched for someparticular feature or set of features, such as, “highlight positions” onthe eye, which typically represent specular reflections off the iris.The image is analyzed to remove distracting points on glasses, byeliminating long, thin specular reflections. The histogram within theeye region is equalized to increase contrast. The position is refinedusing a circular template in a very small area around the initialestimate.

The user first looks into the camera center and then at a calibrationpoint P whose 3D location is known. This gives 2D iris locations m₁ andm₂, respectively, which are then converted into normalized unit vectorsA and B. Two points are sought: E (the eyeball center) along vector A;and E′ (the iris center) along vector B, such that: the distance betweenE and E′ is r (eyeball radius), and the vector between them points at P.

The first calibration point is used to get the B vector. Once t_(a) isobtained, A is scaled by this value and get a 3D eyeball center estimatefor a given radius. For each eyeball estimate (and correspondingradius), the gaze estimation error across all calibration points isobtained. The estimate selected is the estimate with the smallest error.Of course, various optimization criteria can be used to select the gazeposition. For example, if there are a limited number of options, thegaze position estimation may be selected based on a history, context,prediction (based on other factors) or statistics, in any combination orsub-combination thereof. Alternately, the system may provide userfeedback and be adaptive based on the feedback.

The basic algorithm assumes that the eyeball center (E), the 3D iriscenter (E′), and the 3D gaze point (P) are all coplanar, which may notbe true if the user's head moves during the calibration procedure. Thus,the vectors should be adjusted for head rotation and translation beforeperforming the calibration calculations.

Due to the optical/visual axis offset as well as user error duringcalibration, a secondary, iterative refinement procedure should beperformed. This procedure preferably encompasses a position/radiusbinary search, wherein the fovea position is calculated as intersectionof original A vector with final eyeball sphere, and stored as an offsetfrom eyeball center. The final 3D eyeball center is given as an offsetfrom the 3D head point. The eyeballs are then translated/rotated withthe head.

To get the iris contour points, the following algorithm is executed. Asmaller search region around the iris position is defined, and thegrayscale image blurred with a Gaussian filter. Gradient magnitudes anddirections are then extracted.

Given a normalized 2D vector H that goes from the iris center estimateto the 2D eyeball center, shoot rays R_(i) outwards around H (one rayper degree). For all pixels (within search region) along each ray, ascore may be computed:

score_(i,j) =m _(i,j)*(dot(H,D _(i,j))>0.5)  (13)

where i is the ray index,

j is the pixel index,

m_(i,j) is the gradient magnitude, and

D_(i,j) is the normalized gradient direction vector (from dark to lightpixels).

The highest scoring pixel along each ray is chosen as a potential iriscontour point. Duplicate points (caused by overlapping rays) areremoved, giving N′ iris contour points. To eliminate possible eyelidedges, only keep pixels with horizontal gradient angles (verticaledges); this gives us our final N iris contour points. The confidencevalue for contour is computed as N/N′.

The iris center and contours are detected, and converted to perspectivevectors. These points are then mapped to the eyeball sphere.

The current eyeball center is subtracted and the vectors are normalizedto ultimately get V (iris center) and all C_(i) vectors (iris contours).The optical axis G is sought such that: 1) it is parallel to V, and 2)the dot product of G and each C_(i) is aveDot.

Thus, the following linear equations are solved:

$\begin{matrix}{{\begin{bmatrix}C_{0}^{X} & C_{0}^{Y} & C_{0}^{Z} \\\ldots & \ldots & \ldots \\C_{N}^{X} & C_{N}^{Y} & C_{N}^{Z} \\V^{X} & V^{Y} & V^{Z} \\\ldots & \ldots & \ldots \\V^{X} & V^{Y} & V^{Z}\end{bmatrix}\begin{bmatrix}G^{X} \\G^{Y} \\G^{Z}\end{bmatrix}} = \begin{bmatrix}{aveDot} \\\ldots \\{aveDot} \\1 \\\ldots \\1\end{bmatrix}} & (13)\end{matrix}$

Parameter aveDot is found by getting the average dot product of allC_(i) vectors from the “look-into-camera” phase of calibration and anapproximation of the optical axis (use intersection of iris centerperspective ray with the eyeball).

To get the visual axis, the fovea offset is rotated based on the opticalaxis G. The optical axis is intersected with the eyeball sphere to get anew estimate for the 3D iris center, and take the normalized vector fromthe fovea to this new iris center as our final gaze direction.

In order to perform screen mapping, the screen's 3D position, size, andorientation relative to the camera are determined or assumed to beknown. Given a gaze starting point and vector, mapping is a simpleray-plane intersection process. The average position of the two eyeballcenters is used as the starting point and the average of the two visualaxis vectors as the gaze direction.

A two (multiple)-camera system may be provided that can detect the faceand eyes and allows for translational movement freedom, withoutresorting to infrared light, stereo-camera setups, or other complexhardware solutions. Moreover, an eyeball center and fovea offsetextraction procedure and gaze estimation approach may be employed, bothof which are fully capable of dealing with head pose adjustments.

The screen may be located relative to the camera, and uses points on thescreen itself for calibration. These points are adjusted for therotation of the active camera during calibration.

The system obtains information about a subject's visual interest in anobject or visual scene. For example, the subject may be a shopper andthe visual scene may comprise items on display. The method may furthercomprise determining duration of point of gaze on an item; anddisclosing information about the item when the duration of point of gazeexceeds a threshold duration. Information may be obtained about thevisual interest of subjects for an object on display, such as a productor advertisement, and the information used to determine the cost ofdisplaying that object or advertisement. The method may comprisedetermining whether the location of the point of gaze is on the item,and disclosing information about the item to the subject when thelocation of the gaze is or has been on the item; determining duration ofpoint of gaze on an item, wherein disclosing depends on length of suchduration; disclosing information about location and/or duration of pointof gaze on an item to a third party; and/or using said information todetermine a cost of displaying said item. Moving objects may be trackedby the subject's eye. The point of gaze of a user on an object may beidentified, as a control signal to a mechanical device that moves theobject. The object may, for example, move according to the user's gaze,or portions of the object, e.g., a robot, move based on the user'sattention. The user control may be based on the point of gaze, time ofgaze, gaze movement, dynamic gaze endpoints, dynamic gaze parameters(speed, acceleration, direction, etc.), etc. Further, the gaze ofmultiple concurrent users may be tracked, with control of one or moreobject or portions of objects in response to the multiple concurrentusers. Gaze may be used to control a device or appliance, or to controla flow of information, or a relationship, between multiple devices. Forexample, the target device of a “universal” remote control may bedetermined based on a user's gaze direction.

Gaze may also be used to control a visual user interface, with a two orthree dimensional space cursor following the gaze direction. Differentgestures, e.g., hand, face or head, eye or eyelid, voice, may be used tocontrol actions, depth ambiguity, and/or provide other spatial ornon-spatial control inputs. The gestures may be received using the sameoptical system as the gaze, or through a different system. For example,a Microsoft Kinect or similar scene or motion capture device may be usedto acquire physical gestures and audio inputs, which may be processedalong with the eye gaze information. In a graphic user interfaceembodiment, the point of gaze or one or more users of a graphical userinterface may be determined, and the appearance of information on thegraphical user interface controlled in accordance therewith. In ahand-held communication device embodiment, one or more cameras facingthe user may acquire gaze information, to perform user interfacefunctions such as dialing, typing, smart-phone graphic user interfaceinput, etc. Actions may be indicated special blinks or blink sequences,long duration stare, or non-eye gesture or input, such as manual orfacial gesture, voice or audio, or the like.

According to the invention, a computer may be programmed to execute themethod steps described herein. The invention may also be embodied asdevice or machine component that is used by a digital processingapparatus to execute the method steps described herein. The inventionmay be realized in a critical machine component that causes a digitalprocessing apparatus to perform the steps herein. Further, the inventionmay be embodied by a computer program that is executed by a processorwithin a computer as a series of executable instructions. Theinstructions may reside in random access memory of a computer, or on ahard drive, optical drive of a computer, flash memory, or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a system according to the present invention;

FIG. 2 shows the system of FIG. 1 in use;

FIG. 3 shows stage 1 of a calibration procedure;

FIG. 4A shows “iris disk” concept: shorter vectors are the “iris contourvectors,” while the longer vector is the computed (optical axis) gazedirection;

FIG. 4B shows the optical vs. visual axis;

FIG. 5 shows a properly scaled gaze test, captured with a web camera, inwhich the numbers represent each cluster when the user looks at thecenter of blocks in positions from left to right, row by row from top tobottom;

FIG. 6 shows a gaze test captured with a web camera, in which the largewhite lines are the gaze directions (visual axis);

FIG. 7 shows a gaze direction test with active camera images; and

FIG. 8 shows a typical prior art hardware configuration of a networkedcomputer system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The complete system consists of five different stages: face detection,eye area detection (wide-angle view), camera control, iris detection(narrow-angle view), and gaze calibration/estimation (narrow-angleview). The first three are part of one program, while the last two arepart of another; these two programs run on separate computers. Accordingto one embodiment, an IEEE 1394 camera is used for the wide-angle view;images from this camera are used for face detection. Once a face and eyearea center are detected, the detection program controls a SONYSNC-RZ30N camera, which can pan ±170° and tilt from −90° to +25°. Italso has a 25× optical zoom. This camera gives us a close-up view of theface (640×480 images at approximately 15 to 30 fps), which can then beused by the eye detection program. FIG. 1 depicts the systemcomposition, while FIG. 2 depicts the system in action. In theintegrated system, the gaze estimation uses the active camera view, andthe iris centers and contours are extracted from the active camera imagestream. Then, after gaze calibration, the gaze direction and startingpoint (i.e. eyeball centers) is estimated and then mapped to screencoordinates.

Face Detection

An appearance-based technique is employed, based on the work by Violaand Jones [14] for face detection. To improve the robustness of the facedetector, a linear-time mechanism is used to make the system invariantto variable lighting conditions: all features are scaled by a ratio ofthe average gray-level intensity of the training samples over theaverage gray-level intensity of the current search region. The integralimage is used to efficiently compute feature block intensity levels. Thebest Haar-like features are selected with Adaboost; we then usedInformation Gain in the Gain Ratio as a metric of usefulness. Thedetails of the developed face detector can be found in [7].

Eye Detection (from the Static Camera View)

Once the face is detected, eye detection is performed using theso-called topographic features of eyes [15]. The basic idea is to createa terrain map from the gray-scale image (effectively treating it like acontinuous 3D surface) and extracting “pit” locations as pupilcandidates. The actual eye pair is chosen using a Gaussian Mixture Model(GMM) and certain heuristics (e.g. the eye candidates cannot bevertical). The approximate center of the two detected eye candidates isused as the focus of the pan-tilt-zoom camera. Note the mutualinformation tracking approach presented in [15] is not used, and insteadthe eyes detected once every time the face is detected in the wide-angleview.

Iris Detection (from the Active Camera View)

The above stage provides an approximate localization of eyes, allowingthe active camera to zoom into the region of interest. To detect theaccurate positions of irises, we propose a fine detection approach asfollows.

The red channel of the image is preferably employed, since the iris(unlike the surrounding skin areas) generally has very low red intensityvalues [13]. “Highlight positions” on the eye (corresponding to specularreflections off the iris) are searched; these are regions containingenough dark pixels to be considered part of the iris while still havinga high enough standard deviation to contain specular reflection points.To remove distracting points on glasses, specular reflections that arelong and thin (unlike iris highlights, which are generally equal inwidth and height) are eliminated. Unlike Vezhnevets and Degtiareva [13],the histogram is equalized within the eye region to increase contrast.To determine the proper thresholds and parameters, information from 7video sequences collected using the active camera are analyzed. Finally,the initial iris estimate is refined using a circular template in a verysmall area around the initial estimate.

Gaze Calibration (from the Active Camera View)

The calibration procedure has two stages: the first acquires an estimatefor the 3D eyeball center and radius, and the second iteratively refinesour initial estimate while also extracting the position of the fovea onthe eyeball surface. Note that each eyeball is handled independentlyduring calibration.

Stage 1 Calibration (Initial Estimate)

At this point, the 2D iris positions are obtained, and the camera'sfocal length assumed as known; given a 3D eyeball radius r, an estimatefor the 3D eyeball center E is sought.

The camera center is considered the origin of a 3D coordinate system andthe camera view direction as the z axis. Given a 2D pixel position andthe camera's focal length, a 3D vector can be obtained from the cameracenter through every 3D position that maps to our given 2D pixel point.This can be done simply by constructing a “world image plane,” a 3Dplane which is perpendicular to the camera's view axis and is far awayenough such that 3D points in the plane have the same x and ycoordinates as their projected 2D points. A 2D pixel point can then beconverted to a 3D vector by setting its z coordinate to be the z depthof the world image plane.

If the user is looking straight into the camera, it is assumed that theeyeball center must be somewhere along a 3D vector starting at thecamera center and going through the 2D iris center; that is, the gazedirection goes from the 3D eyeball center E to the 3D iris center E′(this vector is known as the “optical axis”). Granted, this is notstrictly true, since the correct gaze direction (called the “visualaxis”) is a vector from the fovea (on the back of the eye) through thepupil [5], and this visual axis is offset from the optical axis byapproximately 4-8° [4]. However, this will be corrected for in Stage 2.

The user first looks into the camera and then at a calibration point Pwhose 3D location is known. This gives the 2D iris locations m1 and m2,respectively. These points are then converted into normalized vectors Aand B. Two points are sought, E (the eyeball center) along vector A andE′ (the iris center) along vector B, such that the distance between themis r (the radius of the eyeball) and the vector between them points atP. FIG. 3 illustrates this idea.

Let t_(a) and t_(b) represent the lengths such that At_(a)=E andBt_(b)=E′; the first constraint may be expressed as follows:

∥At _(a) −Bt _(b) ∥=r  (1)

Point E′ (or Bt_(b)) is the point of intersection between C=At_(a)−P andB. This is equivalent to the point of intersection between B and a planedetermined by point P and normal N=(A×B×C). So, the second constraint isas follows:

$\begin{matrix}{t_{b} = \frac{N\; \bullet \; P}{N\; \bullet \; B}} & (2)\end{matrix}$

Given above equations (1) and (2) with two unknowns t_(a) and t_(b), thefollowing quartic formula is derived, and solved for t_(a):

St _(a) ⁴ +Tt _(a) ³ +UT _(a) ² +Vt _(a) +W=0  (3)

S=Y ²  (4)

T=−2TZ−2(A*B)XY  (5)

U=Z ²+2(A*B)XY−r ² y ² +x ²  (6)

V=2r ² YZ  (7)

W=−r ² Z ²  (8)

X=(A×B×A)*P  (9)

Y=(A×B×A)*B  (10)

Z=(A×B×P)*B  (11)

Once t_(a) is obtained, A can be scaled by this value and a 3D eyeballcenter estimate obtained for a given radius. Although a standard eyeballradius might be employed, instead a range of 1.1 cm to 1.4 cm is cycledin 1/10th millimeter increments, and an eyeball estimate obtained foreach radius size. This corresponds approximately to the natural range ofeyeball radius sizes found in humans (1.2 cm to 1.3 cm) [5].

During the calibration procedure, the user looks into the camera first,and then at four calibration points. The first calibration point is usedto get the B vector. For each eyeball estimate (and correspondingradius) and each of the four calibration points, the gaze estimationapproach used to determine the estimated point of regard and get itsdistance from the true gaze (calibration) point. These error distancesare added together, and the eyeball estimate (and radius) with thesmallest error is chosen.

Note that this approach assumes that eyeball center (E), 3D iris center(E′), and 3D gaze point (P) are all coplanar, which may not be true ifthe user's head moves during the calibration procedure; thus, thevectors adjusted for head rotation and translation before performing thecalibration calculations.

Stage 2 Calibration (Refinement and Fovea Location)

Due to the optical/visual axis offset (as well as user error duringcalibration), the initial estimates can be off slightly from their trueposition. Therefore, a secondary, iterative refinement procedureemployed that uses a binary search to find the best eyeball centerwithin ±5 cm of our initial estimate (to a precision of 1/100th of amillimeter). The radius search is refined simultaneously, using the samerange as before, but also with 1/100th millimeter precision.

Finally, another binary search is performed, this time moving theeyeball position up and down (within 2.5 mm of the current estimate).The fovea is assumed to lie along the A vector, and its positionobtained by intersecting A with the sphere centered at the final eyeballcenter estimate.

The 3D eyeball center is thus obtained (which can be rotated andtranslated with head position and pose information), the 3D eyeballradius, and the fovea point (stored as an offset from the eyeballcenter). 5 sample frames are used for each calibration point, includingthe look-into-camera stage.

Gaze Estimation (from the Active Camera View)

For a given frame, the eyeball center position adjusted based on thecurrent head pose and position. Using the 2D iris center, the iriscontour points are sought and mapped to (and the iris center) theeyeball sphere, the optical axis determined, the fovea point rotatedaccordingly (since its location is dependent on eye position androtation only), the new (3D) iris center computed from the optical axis,and finally the visual axis obtained as the vector from the fovea to thenew iris center.

To obtain the iris contour points, the following eight steps areperformed: (1) Define a smaller search region around the iris positionand blur the grayscale image with a 5×5 Gaussian filter; (2) Extractgradient magnitudes and directions; (3) Given a normalized 2D vector Hthat goes from the iris center estimate to the 2D eyeball center, shootrays R_(i) outwards ±125° around H (one ray per degree); (4) For allpixels (within search region) along each ray, computescore_(i,j)=m_(i,j)*(dot(H,D_(i,j))>0.5), where i is the ray index, j isthe pixel index, m_(i,j) is the gradient magnitude, and D_(i,j) is thenormalized gradient direction vector from dark to light pixels; (5) Thehighest scoring pixel along each ray is chosen as a potential iriscontour point, similar to [8]; (6) Remove duplicate points (caused byoverlapping rays), giving N′ iris contour points; (7) To eliminatepossible eyelid edges, only keep pixels with gradient angles between[−35°, 35°], [145°, 180°], and [445°, −180°] (vertical edges only); thisgives the final N iris contour points; (8) Compute confidence value forcontour as N/N′.)

The 2D iris contour points are mapped to the eyeball sphere byconverting them into 3D perspective vectors and intersecting them withthe current eyeball sphere. A normalized vector going from the eyeballcenter to one of those intersection points is referred to as an “iriscontour vector” C_(i). Before performing gaze estimation, the 3D irisradius on the eyeball is estimated (or rather, the average dot productbetween the optical axis and each C_(i)). The information extractedduring the look-into-camera phase of the calibration procedure is used;note that an approximation of the optical gaze vector can be extractedby intersecting the 2D iris center with the eyeball sphere, subtractingthe eyeball center, and normalizing the result, giving us vector V. Theaverage of the dot products (aveDot) between V and each C_(i) areobtained. In this way, the “iris disk” is defined. See FIG. 4A for anillustration of this concept. This unique approach of mapping 2D contourpoints directly onto the 3D eyeball sphere allows for efficientdetection of the gaze direction. This process is discussed in moredetail below.

Given a normalized 2D vector H that goes from the iris center estimateto the 2D eyeball center, shoot rays R_(i) outwards around H (one rayper degree). For all pixels (within search region) along each ray, ascore may be computed:

score_(i,j) =m _(i,j)*(dot(H,D _(i,j))>0.5)  (12)

where i is the ray index,

j is the pixel index,

m_(i,j) is the gradient magnitude, and

D_(i,j) is the normalized gradient direction vector (from dark to lightpixels).

The highest scoring pixel along each ray may be chosen as a potentialiris contour point. Duplicate points (caused by overlapping rays) areremoved, giving N′ iris contour points. To eliminate possible eyelidedges, only pixels with gradient angles are kept, providing the final Niris contour points. The confidence value for contour is computed asN/N′.

The iris center and contours are detected, and converted to perspectivevectors. These points are mapped to the eyeball sphere.

For gaze estimation, the iris center and contours are detected, andthese points mapped to the eyeball sphere to ultimately get V (iriscenter) and all C_(i) vectors (iris contours), respectively. The opticalaxis G is sought, such that 1) it is parallel to V and 2) the dotproduct of G and each C_(i) is aveDot. Thus, we solve the followinglinear equations:

$\begin{matrix}{{\begin{bmatrix}C_{0}^{X} & C_{0}^{Y} & C_{0}^{Z} \\\ldots & \ldots & \ldots \\C_{N}^{X} & C_{N}^{Y} & C_{N}^{Z} \\V^{X} & V^{Y} & V^{Z} \\\ldots & \ldots & \ldots \\V^{X} & V^{Y} & V^{Z}\end{bmatrix}\begin{bmatrix}G^{X} \\G^{Y} \\G^{Z}\end{bmatrix}} = \begin{bmatrix}{aveDot} \\\ldots \\{aveDot} \\1 \\\ldots \\1\end{bmatrix}} & (13)\end{matrix}$

Note that aveDot, V, and the constant 1 are repeated in their respectivematrices N times (once for each contour vector).

To get the visual axis, the fovea offset is rotated based on the opticalaxis G. The optical axis is intersected with the eyeball sphere to get anew estimate for the 3D iris center, and the normalized vector takenfrom the fovea to this new iris center as the final gaze direction (seeFIG. 4B).

It is preferable to average the eyeball centers and the gaze directionsover several frames to get stable estimates (our current buffer is forthe eyeball is 10 frames, while 3 frames are used for the gazedirection). Moreover, the gaze direction is weighed by the confidencevalue from the contour extraction.

Once the current 3D eyeball position and gaze vector are obtained, thisinformation is mapped to screen coordinates. It is assumed that thescreen's 3D position, size, and orientation are already known, and sothe mapping is a simple ray-plane intersection. The average position ofthe two eyeball centers is used as the starting point and the average ofthe two visual axis vectors as the gaze direction.

For all stages of calibration and gaze estimation, a given sample ofdata is not used unless its confidence value exceeds 10% (which israther low but does at least get rid of utterly erroneous values).Moreover, while the calibration and gaze values are computed for eacheye separately, a sample is not used unless both eyes have high enoughconfidence values.

A gaze and point of gaze estimation experiment is performed wherein theuser was asked to look at 20 gaze markers on the screen (effectively,the center of each brick in a 5×4 grid). To ensure that the calibrationpoints were at known locations relative to the camera, a Logitech OrbitAF web camera was used in a special rig, with a yardstick attached forthe purpose of evaluating the calibration and gaze estimationapproaches. A close-view face image captured from a distance by anactive camera (using an optical zoom) is approximately equivalent to theface image captured by a static camera close the subject, and the effectof a zoom lens simulated by positioning the user's head about 30 to 40cm away from the camera. Camera images were 640×480 pixels. Head poseinformation was extracted using an existing face library [6]. Eachmarker was gazed at for 2-4 seconds (about 20 gaze samples for eachmarker on average).

FIG. 5 shows the estimated gaze positions, while Table 1 lists thevariability of the gaze direction for a given gaze point(“intra-cluster”), and the separation (again, in gaze direction angles)between clusters (“inter-cluster”). The latter is computed as the meanangular distance between the average gaze directions of neighborclusters horizontal and vertically. Finally, FIG. 6 shows some samplesof the gaze estimation results with the user's head rotated.

The ordering of the gaze points matches the pattern of the grid, and theclusters themselves are fairly compact. We believe that a furthercorrected calibration between the camera and the screen could improvethe result.

TABLE 1 Intra- and inter-cluster separation (in degrees) Min Max MeanStd Dev Intra-cluster 0.0684° 4.9158° 1.0889° 0.6710° Inter-cluster2.3292° 16.4482° 8.0991° 4.7793°

The present system has following major advantages. It uses a regularvisible optical camera with diffuse illumination, and it does notrequire structured illumination, infrared images, or other specializedhardware. It provides 3D eye ball gaze axis estimation, and it is 3Dhead pose invariant. The system provides a feasible method for gazetracking in a distance from the cameras. The system compensates forslight inaccuracies in iris center and contour points by using both inan LSQ approach.

The calibration approach of the present method proceeds by determiningthe 3D eyeball center, radius, and fovea position. The gaze is thenestimated by creating a 3D “iris disk” out of iris contour points andiris center, deriving the optical axis, and rotating the fovea to getthe visual axis. In a computer user interface system, the visual axismay then be mapped to a display screen, or otherwise used as part of auser input paradigm.

The present system and method maps a set of 2D points to a 3D eyeball,deriving the optical axis directly, and is therefore efficient. Thesystem provides gaze estimation in a manner which is head poseinvariant.

The present gaze estimation technology may be used for passivemonitoring of persons, to determine interest, distraction, or focus, forexample. The technology may be applied to individuals or to groups.Likewise, the technology provides an additional possibility for userinput to a visual user interface, especially where the input sought isstream of use focus rather than a discrete object.

The technology thus may be used in interactive advertising or otherinformation optimization schemes, where the user attention focus overtime provides useful information, and suitably permits user controleither explicitly or implicitly.

Another aspect of the technology is that it provides an additionaldegree of freedom for a user to control a system, especially where thehands are unavailable or already and/or independently employed.

Because the gaze direction of one or more users is available andemployed, the technology is particular useful in environments where theuser is expected to focus his or her eyes on a particular object, andtherefore by monitoring the user's gaze direction, the location of theobject of the user's attention can be inferred. Thus, where a user isinteracting with a television or media display, the user's gaze may beused to provide a control input, to supplement or replace a “remotecontrol”. The gaze direction may also be used to trigger a retrievaland/or display of additional information. For example, a browserhyperlink may be exercised by a significant user attention on thehyperlink trigger. In other cases, a user help screen or popup balloonmay be generated in dependence on a user's gaze.

The gaze direction may also be used in place of manipulative interfaces.For example, a smart phone may be provided which receives userselections, such as dialing commands, based on a user's visual focus ona number region on the display, as determined by a rear-facing camera onthe phone.

The system may be adaptive in operation. For example, where there is lowambiguity in the gaze direction, e.g., the user has only a fewwell-spaced discrete object to focus on, the system may select thenearest object to the estimated gaze position, and then providecalibration to the algorithm then presuming that the low ambiguitylocation is the exact location of gaze. Thus, during usage, the systemmay be tuned. On the other hand, where a historical analysis indicates anormal margin for error, and the estimated gaze direction is consistentwith the object location within the margin for error, the adaptiveupdate may be prevented, or applied with a low weighing, to avoidovercorrection for possibly noisy feedback data.

The system may be predictive, for example using a Kalman filter topredict endpoint in a dynamic gaze change. On the other hand, certaingaze direction shifts may be ignored for short periods, consistent withnormal human gaze behaviors. For example, a human may sometimes lookaway from a focal object during thought or interruption. However, insome cases, it is preferred that the cursor remain at the earlierlocation during the interruption or hiatus. In cases where a user'sattention is split between multiple tasks, it may be preferable todefine multiple cursors, which may be concurrently active orsemi-active, and retain the last state prior to a switch of focus.

The gaze direction may be used in conjunction with other user inputs,such as speech, manual input, pointing device input, hand gestures, handpointing, body gestures, facial expressions or gesticulations, or thelike.

Hardware Overview

According to a preferred embodiment, the gaze direction determinationsystem executes on a Microsoft Windows® system, using Windows XP, Vistaor Windows 7 (64-bit), having an Intel Core-2 Duo (2.0 GHz) equivalentor greater CPU, greater than 2 GB RAM, an NVIDIA graphics cardsupporting CUDA 3.1.9 or greater, at least 300 MB free hard disk, and aUSB webcam.

FIG. 8 (see U.S. Pat. No. 7,702,660, expressly incorporated herein byreference), shows a block diagram that illustrates a generic computersystem 400 upon which an embodiment of the invention may be implemented.Computer system 400 includes a bus 402 or other communication mechanismfor communicating information, and a processor 404 coupled with bus 402for processing information. Computer system 400 also includes a mainmemory 406, such as a random access memory (RAM) or other dynamicstorage device, coupled to bus 402 for storing information andinstructions to be executed by processor 404. Main memory 406 also maybe used for storing temporary variables or other intermediateinformation during execution of instructions to be executed by processor404. Computer system 400 further includes a read only memory (ROM) 408or other static storage device coupled to bus 402 for storing staticinformation and instructions for processor 404. A storage device 410,such as a magnetic disk or optical disk, is provided and coupled to bus402 for storing information and instructions.

The computer system may also employ non-volatile memory, such as FRAMand/or MRAM.

The computer system may include a graphics processing unit (GPU), which,for example, provides a parallel processing system which is architected,for example, as a single instruction-multiple data (SIMD) processor.Such a GPU may be used to efficiently compute transforms and otherreadily parallelized and processed according to mainly consecutiveunbranched instruction codes.

Computer system 400 may be coupled via bus 402 to a display 412, such asa liquid crystal display (LCD), for displaying information to a computeruser. An input device 414, including alphanumeric and other keys, iscoupled to bus 402 for communicating information and command selectionsto processor 404. Another type of user input device is cursor control416, such as a mouse, a trackball, or cursor direction keys forcommunicating direction information and command selections to processor404 and for controlling cursor movement on display 412. This inputdevice typically has two degrees of freedom in two axes, a first axis(e.g., x) and a second axis (e.g., y), that allows the device to specifypositions in a plane.

As discussed above, the present invention provides an alternate orsupplemental user input system and method, which may advantageously beused in conjunction with other user interface functions which employ thesame camera or cameras.

The invention is related to the use of computer system 400 forimplementing the techniques described herein. According to oneembodiment of the invention, those techniques are performed by computersystem 400 in response to processor 404 executing one or more sequencesof one or more instructions contained in main memory 406. Suchinstructions may be read into main memory 406 from anothermachine-readable medium, such as storage device 410. Execution of thesequences of instructions contained in main memory 406 causes processor404 to perform the process steps described herein. In alternativeembodiments, hard-wired circuitry may be used in place of or incombination with software instructions to implement the invention. Thus,embodiments of the invention are not limited to any specific combinationof hardware circuitry and software.

The term “machine-readable medium” as used herein refers to any mediumthat participates in providing data that causes a machine to operationin a specific fashion. In an embodiment implemented using computersystem 400, various machine-readable media are involved, for example, inproviding instructions to processor 404 for execution. Such a medium maytake many forms, including but not limited to, non-volatile media,volatile media, and transmission media. Non-volatile media includes, forexample, semiconductor devices, optical or magnetic disks, such asstorage device 410. Volatile media includes dynamic memory, such as mainmemory 406. Transmission media includes coaxial cables, copper wire andfiber optics, including the wires that comprise bus 402. Transmissionmedia can also take the form of acoustic or light waves, such as thosegenerated during radio-wave and infra-red data communications. All suchmedia must be tangible to enable the instructions carried by the mediato be detected by a physical mechanism that reads the instructions intoa machine. Wireless or wired communications, using digitally modulatedelectromagnetic waves are preferred.

Common forms of machine-readable media include, for example, hard disk(or other magnetic medium), CD-ROM, DVD-ROM (or other optical ormagnetoptical medium), semiconductor memory such as RAM, PROM, EPROM,FLASH-EPROM, any other memory chip or cartridge, a carrier wave asdescribed hereinafter, or any other medium from which a computer canread. Various forms of machine-readable media may be involved incarrying one or more sequences of one or more instructions to processor404 for execution.

For example, the instructions may initially be carried on a magneticdisk of a remote computer. The remote computer can load the instructionsinto its dynamic memory and send the instructions over the Internetthrough an automated computer communication network. An interface localto computer system 400, such as an Internet router, can receive the dataand communicate using a wireless Ethernet protocol (e.g., IEEE-802.11n)to a compatible receiver, and place the data on bus 402. Bus 402 carriesthe data to main memory 406, from which processor 404 retrieves andexecutes the instructions. The instructions received by main memory 406may optionally be stored on storage device 410 either before or afterexecution by processor 404.

Computer system 400 also includes a communication interface 418 coupledto bus 402. Communication interface 418 provides a two-way datacommunication coupling to a network link 420 that is connected to alocal network 422. For example, communication interface 418 may be anintegrated services digital network (ISDN) card or a modem to provide adata communication connection to a corresponding type of telephone line.As another example, communication interface 418 may be a local areanetwork (LAN) card to provide a data communication connection to acompatible LAN. Wireless links may also be implemented. In any suchimplementation, communication interface 418 sends and receiveselectrical, electromagnetic or optical signals that carry digital datastreams representing various types of information.

Network link 420 typically provides data communication through one ormore networks to other data devices. For example, network link 420 mayprovide a connection through local network 422 to a host computer 424 orto data equipment operated by an Internet Service Provider (ISP) 426.ISP 426 in turn provides data communication services through the worldwide packet data communication network now commonly referred to as the“Internet” 428. Local network 422 and Internet 428 both use electrical,electromagnetic or optical signals that carry digital data streams. Thesignals through the various networks and the signals on network link 420and through communication interface 418, which carry the digital data toand from computer system 400, are exemplary forms of carrier wavestransporting the information.

Computer system 400 can send messages and receive data, includingprogram code, through the network(s), network link 420 and communicationinterface 418. In the Internet example, a server 430 might transmit arequested code for an application program through Internet 428, ISP 426,local network 422 and communication interface 418.

The received code may be executed by processor 404 as it is received,and/or stored in storage device 410, or other non-volatile storage forlater execution.

U.S. 2012/0173732, expressly incorporated herein by reference, disclosesvarious embodiments of computer systems, the elements of which may becombined or subcombined according to the various permutations.

In this description, several preferred embodiments were discussed. It isunderstood that this broad invention is not limited to the embodimentsdiscussed herein, but rather is composed of the various combinations,subcombinations and permutations thereof of the elements disclosedherein. The invention is limited only by the following claims.

REFERENCES Each of which is Expressly Incorporated Herein by Reference

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What is claimed is:
 1. A method for estimating an eye gaze direction asa vector from a fovea of an eye, through a center of an iris, to anobject upon which gaze is directed, based on a facial image, comprising:receiving facial image by at least one processor, and based on at leastthe facial image, an anatomical model of the eye, and an adaptivecomputational model stored in a memory: estimating the center of theiris; estimating a three dimensional center and size of the eye tothereby define an optical axis through the center of the iris and thethree dimensional center of the eye; estimating a position of the foveaof the eye, displaced from the optical axis of the eye; estimating aneye gaze direction along the vector; and receiving calibrationinformation representing an error between the estimated eye gazedirection and a gaze target; updating the adaptive model to reduce theerror; and outputting information selectively dependent on the estimatedeye gaze direction.
 2. The method according to claim 1, the facial imagecomprises images of a pair of eyes gazing toward a common gaze target,further comprising: detecting the pair of eyes in the facial image; anddetermining a statistical composite estimated eye gaze direction alongthe vector for each eye.
 3. The method according to claim 1, wherein thecenter of the iris is estimate by determining a contour of the iris inthe facial image, and determining the center of the determined contour.4. The method according to claim 1, wherein the facial image isprocessed employing a lighting invariant linear-time process.
 5. Themethod according to claim 4, wherein a set of Haar-like features areselected after employing the lighting invariant linear-time process,using an adaptive boosting process.
 6. The method according to claim 4,further comprising: detecting a face in the facial image by terrainmapping; and extracting pit locations as pupil candidates.
 7. The methodaccording to claim 1, further comprising estimating a position of atleast one eye in the facial image using a Gaussian Mixture Model (GMM)and facial model-based heuristics.
 8. The method according to claim 1,wherein the facial image is processed by the at least one automatedprocessor in color.
 9. The method according to claim 1, furthercomprising searching the facial image for specular reflections.
 10. Themethod according to claim 1, further comprising the facial image toeliminate long, thin specular reflections representing reflections fromeyeglasses.
 11. The method according to claim 1, further comprisingacquiring at least one facial image with the vector directed toward thecamera, and at least one facial image with the vector directed away fromthe camera.
 12. The method according to claim 1, further comprisingiteratively seeking a best estimate of the three dimensional center ofthe eye and the position of the fovea.
 13. The method according to claim1, further comprising estimating a rotation of the eye representing anoffset of the position of the fovea from the optical axis of the eye.14. The method according to claim 1, further using the outputtedinformation to control a graphic user interface.
 15. A system forestimating an eye gaze direction vector from a fovea of an eye, througha center of an iris of the eye, to an object upon which gaze isdirected, comprising: an input port configured to receive an electronicfacial image; at least one processor, configured to: receive theelectronic facial image; based on at least the facial image, ananatomical model of the eye, and an adaptive computational model storedin a memory, estimate the center of the iris, a three dimensional centerand size of the eye to thereby define an optical axis through the centerof the iris and the three dimensional center of the eye, estimate aposition of the fovea of the eye, displaced from the optical axis of theeye, and estimate the eye gaze direction along the vector; receivecalibration information representing an indication of an error betweenthe estimated eye gaze direction and a direction to the object; updatethe adaptive model to statistically reduce the error; and generate asignal corresponding to the estimated eye gaze direction; and an outputport configured to communicate information selectively dependent on thesignal.
 16. The apparatus according to claim 15, wherein the at leastone automated processor is configured to search for specular reflectionsoff each eye, the detect a face having a pair of eyes in the image,determine an eye gaze direction for each eye, and determine at least onestatistical composite of the directional vector for each eye torepresent the gaze direction.
 17. The apparatus according to claim 15,wherein the at least one automated processor is configured to determinean iris center V, a set of iris contour vectors C_(i) vectors, and todetermine the optic axis G such that it is parallel to V and the dotproduct of G and each C_(i) is aveDot, using the following linearequations: $\begin{matrix}{{\begin{bmatrix}C_{0}^{X} & C_{0}^{Y} & C_{0}^{Z} \\\ldots & \ldots & \ldots \\C_{N}^{X} & C_{N}^{Y} & C_{N}^{Z} \\V^{X} & V^{Y} & V^{Z} \\\ldots & \ldots & \ldots \\V^{X} & V^{Y} & V^{Z}\end{bmatrix}\begin{bmatrix}G^{X} \\G^{Y} \\G^{Z}\end{bmatrix}} = \begin{bmatrix}{aveDot} \\\ldots \\{aveDot} \\1 \\\ldots \\1\end{bmatrix}} & (13)\end{matrix}$ in which aveDot, V, and the constant 1 are repeated intheir respective matrices N times for N contour vectors C_(i).
 18. Theapparatus according to claim 15, wherein the automated processor isconfigured to: estimate the eye gaze direction by acquiring at least oneimage each of an eye directed looking into at least one camera and ofthe eye directed looking toward at least one calibration point; anditeratively seek a best statistical estimate of the three dimensionalcenter of the eye and the position of the fovea.
 19. The apparatusaccording to claim 15, wherein the automated processor is furtherconfigured to: search for a boundary of the iris of the eye; estimatethe center of the iris based on the boundary of the iris; and rotatingthe an offset location of the fovea from the optical axis of the eye tostatistically reduce the error.
 20. A method for eye gaze vectorestimation, comprising: acquiring facial images; determining a threedimensional iris center of an iris of an eye within the acquired facialimages; estimating a three dimensional center and size of the eye,wherein a position of the fovea of the eye is displaced from an opticaxis of the eye defined by a vector extending from the three dimensionalcenter of the iris through the three dimensional center of the eye;estimating an eye gaze direction along a vector from a predictedposition of the fovea and passing through the three dimensional centerof the iris; and updating a set of stored parameters for estimating atleast the three dimensional center of the eye, size of the eye, and theposition of the fovea, based on acquired facial images when the eye gazedirection is directed toward at least two distinct predeterminedobjects.